Electrosurgical devices configured for use with a dry tip use electrical energy, most commonly radio frequency (RF) energy, to cut tissue or to cauterize blood vessels. During use, a voltage gradient is created at the tip of the device, thereby inducing current flow and related heat generation in the tissue. With sufficiently high levels of electrical energy, the heat generated is sufficient to cut the tissue and, advantageously, to stop the bleeding from severed blood vessels.
Current dry tip electrosurgical devices can cause the temperature of tissue being treated to rise significantly higher than 100.degree. C., resulting in tissue desiccation, tissue sticking to the electrodes, tissue perforation, char formation and smoke generation. Peak tissue temperatures as a result of RF treatment of target tissue can be as high as 320.degree. C., and such high temperatures can be transmitted to adjacent tissue via thermal diffusion. Undesirable results of such transmission to adjacent tissue include unintended thermal damage to the tissue.
Using saline according to the present invention to couple RF electrical energy to tissue inhibits such undesirable effects as sticking, desiccation, smoke production and char formation. One key factor is inhibiting tissue desiccation, which occurs when tissue temperature exceeds 100.degree. C. and all of the intracellular water boils away, leaving the tissue extremely dry and much less electrically conductive. However, an uncontrolled or abundant flow rate of saline can provide too much cooling at the electrode/tissue interface. This cooling reduces the temperature of the target tissue being treated, and the rate at which tissue thermal coagulation occurs is determined by tissue temperature. This, in turn, can result in longer treatment time to achieve the desired tissue temperature for treatment of the tissue. Long treatment times are undesirable for surgeons since it is in the best interest of the patient, physician and hospital, to perform surgical procedures as quickly as possible.
RF energy delivered to tissue can be unpredictable and often not optimal when using general-purpose generators. Most general-purpose RF generators have modes for different waveforms (e.g. cut, coagulation, or a blend of these two) and device types (e.g. monopolar, bipolar), as well as power levels that can be set in watts. However, once these settings are chosen, the actual power delivered to tissue and associated heat generated can vary dramatically over time as tissue impedance changes over the course of RF treatment. This is because the power delivered by most generators is a function of tissue impedance, with the power ramping down as impedance either decreases toward zero or increases significantly to several thousand ohms. Current dry tip electrosurgical devices are not configured to address a change in power provided by the generator as tissue impedance changes or the associated effect on tissue and rely on the surgeon's expertise to overcome this limitation.